Leaky heater core / AC?

[Zerohour3k]

Okay, here's the issue, and a question.

Just bought a new 300D (1983 300D Turbo), that runs pretty damn well. The car is 24+ years old, so it has a few issues.. but in all, not too bad. Rear windows don't work, A/C has a leak somewhere, and he stuck Euro lights on it. I like the city lights and all, but to be honest, I think the Euros make the car look too much like a generic 80's sedan.

Aaaanyway.. back to the issue. The A/C works, and the push-button controls were a refurbed rebuild within the last 35,000 miles. On A/C mode, the thing blows pretty cold (and sometimes TOO cold). Turning down the temp dial to the "white zone" doesn't seem to do too much in regards to making it less frigid in the car, and turning it down into the red zone makes the car smell musty for a little bit. Getting in the car in the morning, the inside windshield has a tiny bit of condensation on it. If I start the car and stick the thing on "EC" mode, it blows out humid air that fogs up my windows even worse. Even starting the car on AC mode will fog them up for a little bit.. before it clears up.

Obviously, this is gonna be one of three possible problems. The A/C hose is clogged, and not letting water drain from the heater core... the heater core leaks, or I have rainwater getting in the car.

Keep in mind that it's been INCREDIBLY humid outside recently, and that probably isn't helping any. If the heater core does have a small leak in it, can I just plug it with one of those "temporary fix" products? Do you guys reccomend any brand in particular? I don't really feel like paying an ungodly amount of cash for a heater core install.